1. Technical Field
This invention relates to a process for obtaining a polyarylene sulfide (referred to hereinafter as PAS) in the form of particles. More particularly, this invention relates to a process for treating a polymer slurry in order to prepare a particulate PAS in the form of a slurry containing in addition a crystalline alkali chloride by reacting an alkyl sulfide with a dichloroaromatic compound in a medium of water and N-methylpyrrolidone (referred to hereinafter as NMP), characterized in that the PAS, the chrystalline alkali chloride as a by-product and NMP are recovered in good yields.
2. Prior Art
Hitherto, there have been proposed many methods for producing PAS, among which methods a typical one involves the reaction of dichlorobenzene and an alkali sulfide in a polar solvent. There have also been reported many proposals with reference to specific reaction conditions and the like therefor.
However, none of these proposals have been successful in isolating the resulting PAS from the medium containing an arylene sulfide oligomer as a by-product of polymerization, and therefore the PAS has been conventionally recovered in the form of powder from the reaction mixtures by the solvent flashing method. Furthermore, the PAS in the form of powder brings about problems such as that when it becomes a product it is easily blown off as dust upon drying because it is a resin having a small particle size (fine powder) with a relatively low bulk density.
For the purpose of avoiding such problems, there have been developed recovering methods of PAS as a polymerization product to separate and recover the PAS more readily. One of such methods is disclosed, for example, in Unexamined Published Japanese Patent Application No. 1536/84. This method comprises polymerizing an alkali sulfide and a dihaloaromatic compound in NMP as a medium, then, for the purpose of separating PAS from the polymer slurry and recovering the medium NMP, adding first a large amount of water to the polymer slurry to dissolve therein most of soluble salts, then filtering PAS, and finally recovering NMP from the aqueous solution of NMP remaining after an arylene sulfide oligomer has been removed. However, the method uses water in a large amount during the separating of PAS, and thus it is not economical to recover NMP by the direct distillation of NMP containing a large amount of water. For this reason, a process for recovering NMP comprising once extracting it with an extracting agent such as n-hexanol and recovering it again by separating from the extracting agent is commonly used. Such a process makes the recovery of NMP complicated and brings about problems such as the treatment of waste water in a large amount.